Tissue products are in almost constant use in daily life. Toilet tissue, facial tissue, and paper towels are examples of tissue products used throughout home and industry.
Tissue products are often made of a single lamina. However, a single lamina tissue product has several drawbacks. For example, a single lamina tissue product will be stiffer than a dual laminae tissue product having the same total basis weight. This increased stiffness results in a consumer perception that the single lamina tissue product is not as soft as the dual laminae tissue product and may, therefore, be less preferred than the dual laminae tissue product.
Furthermore, a dual laminae tissue product having the same total basis weight as a single lamina tissue product can be made to have greater caliper. This increased caliper results in the consumer perception the product has thickness and high quality.
However, dual laminae tissue laminates are subject to the phenomenon of skinning. Skinning occurs when the laminae separate from one another and no longer remain intact to form a unitary laminate.
Skinning may, for example, occur when trying to reduce tissue product packaging and transportation costs. For example, U.S. Pat. No. 4,886,167 issued Dec. 12, 1989 to Dearwester discloses packages of toilet tissue and paper towels compressed orthogonal to the cores to reduce the core volume. This compression of the tissue product may impart shear forces to the laminae and result in skinning.
Several attempts have been made in the art to join the dual laminae in a manner to reduce or minimize skinning. Such attempts have been further complicated by the addition of emollient or lotions to the tissue laminae. For example, U.S. Pat. Nos. 4,481,243 issued Nov. 6, 1984 to Allen and 4,513,051 issued Apr. 23, 1985 to Lavash teach multiple laminae of tissue paper joined by a laminating process. The process embosses the laminae together, but requires the embossed region of the tissue to be free of the emollient. This zone coating of the emollient introduces another variable which must be accounted for during the manufacturing process. Furthermore, such lamination has resulted in a perceived loss of softness of the tissue laminate, contrary to one of the principal reasons for utilizing a dual laminae tissue laminate.
Other attempts to join cellulosic tissue laminae include U.S. Pat. No. 4,770,920 issued Sep. 13, 1988 to Larsonneur. Larsonneur teaches laminae bonded at a pair of juncture lines. The pair of juncture lines include individual pressure spot bonds. The spots bond are formed by the use of thermoplastic low viscosity liquid such as melted wax, paraffin, hot melt adhesive or the like and prevent delamination when the laminae become wet.
The Larsonneur teaching suffers from the drawbacks that multiple lines of spots bond joining the laminae reduces the softness of the laminae. Furthermore, given current environmental concerns, the tissue laminate should preferably break down upon wetting, as, for example, occurs when toilet tissue is disposed of in a sewer system.
Another attempt to produce a dual laminae tissue laminate is illustrated in U.S. Pat. No. 4,885,202 issued Dec. 5, 1989 to Lloyd, et al. Lloyd, et al. teaches a high-strength tissue product having two outer tissue laminae thermally bonded to a central lamina of melt blown fibers. The central lamina consists of polypropylene melt blown fibers and has a basis weight of about ten to fifteen grams per square meter. The central lamina overall thermally bonds the outer tissue laminae together to form a unitary composite structure.
Lloyd, et al. has several drawbacks. The polypropylene central lamina develops good wet strength at the expense of the aforementioned disposability characteristics, desirable for environmental reasons. Further, the overall bonding of the outer laminae to the central lamina decreases softness and requires a significant quantity of the melt blown fibers to be added. And further, adding such a significant quantity of melt blown fibers to the laminate increases the manufacturing costs.
U.S. Pat. No. 4,806,418 issued Feb. 2, 1989 to Sigl teaches joining of lotioned tissue to an overall dusting with nonwater dispersible thermoplastic particles. However, this teaching suffers from the same drawbacks as Lloyd et al.
Also, several attempts have been made in the art to provide an apparatus suitable for adhesively joining two laminae in face-to-face relation. Adhesive Joining of laminae may be accomplished by one of two methods, depositing the adhesive onto the face of one lamina in a spiral pattern, or by meltblowing the adhesive onto the face of one lamina in a random pattern.
For example, U.S. Pat. Nos. 3,911,173 issued Oct. 7, 1975 to Sprague, Jr., U.S. Pat. No. 4,031,854 issued Jun. 28, 1977 to Sprague, Jr. and U.S. Pat. No. 4,098,632 issued Jul. 4, 1978 to Sprague, Jr. teach a spiral adhesive deposition nozzle. These nozzles utilize a circumferentially oriented plurality of air jets to induce a spiral pattern to the filament of adhesive as it is discharged from the nozzle and extrudes to the face of the lamina to be adhesively joined.
U.S. Pat. No. 4,949,668 issued Aug. 21, 1990 to Heindel, et al. discloses an apparatus for depositing hot melt adhesive onto a substrate in a semi-cycloidal pattern. The semi-cycloidal pattern closely controls the cross-directional positioning of the adhesive filament to reduce overspray and waste.
U.S. Pat. Nos. 4,891,249 issued Jan. 2, 1990 to McIntyre and U.S. Pat. No. 4,996,091 issued Feb. 26, 1991 to McIntyre disclose an apparatus and process for generating fluid fiber adhesive droplets and combinations of fibers and droplets. The fibers, droplets and combinations thereof are generated by funneling a cone of pressurized air symmetrically about the adhesive filament. This results in a pattern of randomly laid criss-crossing fiber deposits onto the face of the lamina to be joined.
Clearly a need exists to combine the aforementioned adhesive joining technology with dual laminae tissue to produce a dual laminae tissue laminate which minimizes skinning, but without sacrificing other desired properties such as softness and environmentally facile disposability. Therefore, it is an object of this invention to produce a dual laminae tissue laminate having the laminae adhesively joined in a fashion which does not diminish either softness nor disposability. Further, it is an object of the invention to produce such a tissue laminate which minimizes the use of adhesives, so that manufacturing costs can be controlled.